Turbocharged and supercharged engines may be configured to compress ambient air entering the engine in order to increase power. Compression of the air may cause an increase in air temperature, thus, a charge air cooler may be utilized to cool the heated air thereby increasing its density and further increasing the potential power of the engine. Ambient air from outside the vehicle travels across the CAC to cool intake air passing through the inside of the CAC. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point. Condensate may collect at the bottom of the CAC, or in the internal passages, and cooling turbulators. When torque is increased, such as during acceleration, increased mass air flow may strip the condensate from the CAC, drawing it into the engine and increasing the likelihood of engine misfire.
Example approaches of addressing combustion issues (e.g., misfire) resulting from condensate ingestion involve avoiding condensate build-up. However, the inventors herein have recognized potential issues with such methods. Specifically, while some methods may reduce or slow condensate formation in the CAC, condensate may still build up over time. If this build-up cannot be stopped, ingestion of the condensate during acceleration may cause engine misfire. In addition, based on the engine speed-load condition, as well as the configuration of the engine (e.g., based on whether the engine is a V-engine with distinct banks or an in-line engine), some cylinders may receive more condensate than others, rendering them more prone to combustion issues than others. Other approaches use lean engine operation to provide sufficient airflow to purge condensate to the engine intake. However, engine cylinders with higher water ingestion sensitivity may misfire more often during lean engine operation. In addition, emissions may be degraded. Still other approaches of addressing the combustion issues involve trapping and/or draining the condensate from the CAC. While this may reduce condensate levels in the CAC, condensate is moved to an alternate location or reservoir, which may be subject to other condensate problems such as freezing and corrosion. Further, the reservoir may add component cost and complexity.
In one example, the above described issues may be at least partly addressed by a method for purging condensate from the CAC during vehicle operating conditions. The method may comprise: increasing engine airflow without increasing engine torque, to flow condensate from a charge air cooler into engine cylinders, by fueling some cylinders lean while fueling other cylinders rich and while maintaining an exhaust air-to-fuel ratio of the engine oscillating around stoichiometry. In this way, during purging, fueling of each cylinder may be adjusted based on their water ingestion sensitivity.
In one example, an engine system may include a charge air cooler coupled downstream of a compressor and upstream of an intake throttle. During engine operation, condensate may collect at the charge air cooler. In response to condensate levels being higher than a threshold, purging conditions may be considered met and a clean-out cycle may be initiated to remove the condensate. In particular, the fuel injection of one or more engine cylinders may be shifted from stoichiometric cylinder combustion to lean cylinder combustion with an engine airflow level temporarily increased to provide the lean airflow. The degree of leanness of the lean operating cylinders may be adjusted so that the engine airflow level can be increased to a level so as to blow off condensate into the engine. The engine airflow level may be increased by opening an intake throttle to provide the desired degree of leanness in the lean operating cylinders. At the same time, the remaining engine cylinders may be operated rich, with a degree of richness adjusted based on the degree of leanness of the lean operating cylinders so as to maintain an exhaust air-fuel ratio around stoichiometry. While increasing engine airflow allows the condensate to be delivered to the intake manifold, based on the engine speed-load conditions at the time of the purging, as well as the configuration of the engine, different cylinders may receive different amounts of condensate. In addition, due to the engine configuration, some cylinders may be inherently more sensitive to water ingestion than others. To compensate for this, the controller may selective fuel the engine cylinders rich or lean based on their respective water ingestion sensitivity (which may be inferred based on the amount of condensate they are expected to receive and/or based on prior engine testing data. Specifically, the engine cylinders having lower water ingestion sensitivity (that is, cylinders less prone to ingestion induced misfires) may be selected for operating lean while engine cylinders having higher water ingestion sensitivity (that is, cylinders more prone to ingestion induced misfires) may be enriched.
In one example, the cylinders receiving larger amounts of condensate may have higher water ingestion sensitivity and therefore be enriched, while the cylinders receiving smaller amounts of condensate may have lower water ingestion sensitivity and therefore be enleaned. A degree of richness of the enriched engine cylinders and a degree of leanness of the enleaned engine cylinders may be adjusted so that an exhaust air-to-fuel ratio may be maintained at or around stoichiometry. In addition, while operating the cylinders rich or lean, one or more engine actuators (e.g., spark timing, cam timing) may be adjusted based on the increased airflow so that the engine output is maintained constant. For example, ignition timing of the cylinders operating rich may be advanced from MBT to maintain constant torque. Further, a higher amount of spark advance may be applied to the cylinders operating rich as compared to the cylinders operating lean since the enriched cylinders are likely to incur slow combustion due to the water ingestion. As such, the enrichment also suppresses knock in the enriched cylinders as the rate of condensation ingestion decreases due to the accumulated condensate being consumed.
In this way, condensate may be periodically cleaned from a charge air cooler by blowing off condensate to the engine cylinders. By operating one or more cylinders leaner than stoichiometry, an airflow level to the engine may be sufficiently increased to blow off condensate from the CAC to the engine intake. By concurrently operating other cylinders richer than stoichiometry, an exhaust ratio can be maintained around stoichiometry, providing emissions benefits. By adjusting the fueling of each cylinder during the condensate purging taking into account each cylinder's water ingestion sensitivity, condensate ingestion induced combustion issues, such as misfires, can be better addressed. In particular, by operating the cylinders with higher water ingestion sensitivity rich, lean operation induced misfires in those cylinders during condensate purging is reduced. By increasing engine airflow to purge the condensate to engine cylinders, the need for additional condensate storage components, such as additional reservoirs or tanks is reduced, providing component reduction benefits. By adjusting the cylinder fueling during the purging so that an overall exhaust air-fuel ratio is maintained at stoichiometry, exhaust emissions during the condensate purging is improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.